Microstructure of high (45 wt.%) chromium cast irons and their resistances to wear and corrosion

作者：Tang X H^*; Chung R; Pang C J; Li D Y; Hinckley B; Dolman K

来源：Wear, 2011, 271(9-10): 1426-1431.

DOI：10.1016/j.wear.2010.11.047

• High chromium cast irons
• Microstructure
• Wear
• Corrosion

High chromium cast irons (HCCIs) are widely used in many industrial processes that require materials possessing high resistance to wear and corrosion. In the Alberta oil sands industry, HCCIs are extensively used in slurry pumping systems as well as other processing and handling equipments. However, due to the very harsh mining environment and severe working conditions, conventional HCCIs do not always perform satisfactorily. Great efforts have been made to identify optimum microstructures and chemical compositions in order to effectively tailor HCCIs for improved performance under various operating conditions and minimize maintenance costs. One proposal is to extend the chromium concentration of HCCIs to higher levels.
In this work, six HCCIs containing 45 wt.% of chromium and carbon concentrations ranging from 1 to 6 wt.% with small amounts of silicon and manganese were cast, solution-treated and aged, referred to as 45-series of HCCIs. Their microstructures were characterized using XRD and SEM/EDX. Corresponding resistances to wear, including abrasive wear and erosion-corrosion, and corrosion were evaluated. Microstructures of the 45-series of HCCIs were determined to be hypoeutectic (%C < 2), eutectic (%C similar to 2) and hypereutectic (%C > 2). The ferrous matrix of 45-series of HCCIs was in martensite state. The volume fraction of total carbides increased with increasing the nominal carbon concentration. The formed carbides in the HCCIs with low carbon content (1-3 wt.%) were identified as cubic-face centred M(23)C(6), while hexagonal close packed M(7)C(3) mainly existed in HCCIs with higher carbon contents (5-6 wt.%). In HCCI 45-4, both M(23)C(6) and M(7)C(3) were detected. The wear resistance of 45-series of HCCIs was affected by the volume fraction, types and size of carbides, while their corrosion resistance was dominated by the free chromium content in the matrix and the ratio of volume fraction of carbides to ferrous matrix as well. Further examination showed that primary carbides in HCCI 45-4 had a shell-core structure (shell-M(23)C(6), core-M(7)C(3)). Such a configuration could have a positive effect on the wear resistance of this alloy.

• 出版日期2011-7-29